media: cec: add struct cec_connector_info support

Define struct cec_connector_info in media/cec.h and define
CEC_CAP_CONNECTOR_INFO. In a later patch this will be moved to
uapi/linux/cec.h.

The CEC_CAP_CONNECTOR_INFO capability can be set by drivers, but
cec_allocate_adapter() will remove it again until the public API
for this can be enabled once all drm drivers wire this up correctly.

Also add the cec_fill_conn_info_from_drm and cec_s_conn_info functions,
which are needed by drm drivers to fill in the cec_connector info
based on a drm_connector.

The cec_notifier_(un)register and cec_register_cec_notifier
prototypes were moved from cec-notifier.h to cec.h since cec.h no longer
includes cec-notifier.h. These headers included each other before,
which caused various problems.

Due to these changes the seco-cec driver was changed as well: it
should include cec-notifier.h, not cec.h.

Signed-off-by: Dariusz Marcinkiewicz <darekm@google.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>